8-Ball was bad all along. He was the one that helped the set up of the attempted killing of the main character (the man with no name). As for plot, get some good writers and you might be able to pull it off. Hey, who says it has to me exactly like the game? As for the characters:

Edward Norton- The Man With No Name
Ice Cube- 8-Ball
Joe Pantoliano- Luigi Gotterelli
James Gandolfini- Tony Cipriani
Scott Caan- Joey Leone
Al Pacino- Salvatore Leone
Marisa Tomei- Maria
Matthew Broderick- Donald Love
Michelle Rodriguez- Catalina
Jet Li- Kenji
Lucy Liu- Asuka
Vin Diesel- El Burro
Harvey Keitel- Ray Machowski

I would agree with you that QT would be a good choice for director.